Homeowners and small producers can produce useable apples in South Carolina with minimal insect damage if they know the potential pest problems. Some insecticide applications may be necessary even under the best of conditions.
Pests Attacking the Leaves
There are several pests or groups of pests that feed on apple leaves. Most of these cause minor damage to the tree and are often best left alone. Many natural enemies feed on these pests.
Aphids: Aphids are a fairly common problem on apples. Two major kinds can build up to fairly high numbers during the summer. These are the green apple aphid (Aphis pomi) and the spirea aphid (Aphis spiraecola). Both of these aphids have green bodies. The adult aphids may have wings or be wingless. Aphids are common on the tender young leaves on branch tips and watersprouts. While feeding, the aphids produce honeydew. This is a liquid, which is rich in sugars. Black sooty mold often grows on the honeydew. Aphids have many generations a season.
Aphids are attacked by lady beetles, syrphid fly larvae, and other predators and parasites. In many cases, these beneficial insects may keep the aphids under control if insecticide treatments are avoided.
Insecticidal soap or 1% horticultural oil sprays will help manage aphids with little impact on beneficial insects. See Table 1 for examples of insecticide products.
Mites: Two-spotted spider mites (Tetranychus urticae) and European red mites (Panonychus ulmi) can be serious pests of apples. If mite populations are high, the feeding activity can reduce the quality of the current crop and reduce flower bud set for the following year. While both mites produce the same type of damage, there are some significant differences.
Two-spotted spider mites spend the winter as mature females hiding in protected places on the ground near the tree. In the spring, they begin feeding on the vegetation under the tree. Later, they move up into the tree and begin to feed on the apple leaves.
European red mites spend the winter in the egg stage. The eggs are laid on the tips of the twigs around the rough bud scars. When numbers are high, the twigs will develop a reddish appearance. The mites remain in the tree throughout the season.
Both mites have several generations per season, which makes multiple spray applications necessary.
The most effective treatment for the European red mites (ERM) is a 2% horticultural oil spray (5 tablespoons oil per gallon of water) applied between the green tip stage and tight cluster (before the blooms open) for good early season mite control. This horticultural oil spray will smother both the eggs and the recently hatched mites. Since ERM can go from egg to an adult ready to lay more eggs in about a week, two applications of 1% horticultural oil at 10 to 14 days apart will help control the established populations during late spring and summer.
Similarly, the same early season 2% horticultural oil spray will kill the over-wintering two-spotted spider mite females, and later 1% sprays will greatly reduce summer populations. However, do not spray captan or sulfur within 14 days before or after a horticultural oil spray, as the combination may burn leaves or developing fruit. See Table 1 for examples of insecticide products.
Japanese Beetle: The Japanese beetle (Popillia japonica) adults feed on the leaves during June and July. The beetles feed on the soft leaf tissue and leave the leaf veins, which gives damaged leaves a lacy appearance. Occasionally, they may feed on damaged fruit. The insecticide carbaryl (such as in a fruit tree spray that contains carbaryl as one active ingredient) is very effective against adult beetles. However, repeated use of carbaryl will cause mite populations to increase rapidly. Because of this, it is best to leave the adult beetles alone in most cases. Do not apply carbaryl within 30 days after bloom, as this may cause fruit drop. Additional insecticide sprays for Japanese beetle control are cyhalothrin (lambda or gamma) and zeta cypermethrin. See Table 1 for examples of insecticide products.
Traps may be used to suppress Japanese beetles, but the traps must be placed at least 50 feet away from the plants to be protected. The traps will draw in adult beetles. If the trap is too close to the apple tree, the beetles may stop and feed for a while before entering the trap.
Leafrollers: There are a number of leafrollers (Archips species, Choristoneura rosaceana, and Sparganothis sulfureana) that feed on apple leaves. The biggest problem with leafrollers is that sometimes they will tie the leaves to the fruit and feed on both the surface of the fruit and leaves. Many predators and parasites feed on the leafroller caterpillars. However, if an insecticide treatment is needed, Bacillus thuringiensis (B.t., such as Thuricide) or spinosad will not harm the leafroller’s natural enemies but will kill the young caterpillars. See Table 1 for examples of insecticide products.
Leafminers: The spotted tentiform leafminer (Phyllonorycter species) is an occasional pest on apple trees. Usually, the worst damage occurs on trees that have been heavily sprayed.
The young leafminer caterpillars feed inside the leaf. At first, they feed on the sap present in the leaf. Later, they feed on the leaf tissue. This causes the leaf to pucker, giving the upper leaf surface a tent-like appearance. Heavy mining damage can reduce the current year’s crop quality and reduce flower buds set for the following year. There are two very efficient parasites of this pest. Usually, the parasites keep the leafminers in check. However, if a treatment is necessary, spinosad is a less toxic alternative. It has systemic laminar activity, which means it will penetrate the apple foliage to kill the leafminers that are inside. See Table 1 for insecticide products.
Pests Attacking the Fruit
Codling Moth: The proverbial wormy apple probably has the immature of the codling moth (Cydia pomonella) in it, which is perhaps the number one apple pest in the world. The mature caterpillars (larvae) leave the apples in the fall and spin a silk shelter under loose bark. They spend the winter in this shelter. In the spring, they change into the adult moth. The moths emerge shortly after bloom and lay eggs on leaves near fruit clusters. The larvae enter the young fruit at the calyx end, where the petals were attached. Another generation of moths occurs in July. These moths lay eggs directly on the surface of the fruit. Again, the larvae burrow to the core of the fruit and feed. A third-generation occurs in August.
Insecticide treatments must be directed toward the adult moths or the newly hatched larvae. Once the larvae enter the apples, they are protected. Parasites and predators feed on the eggs and larvae.
Sprays with B.t. (Thuricide) or spinosad will control the codling moth caterpillars if applied before they enter the fruit. See Table 1 for examples of insecticide products. Additionally, codling moth traps can be used to help manage this insect pest (e.g., Gardens Alive, Gemplers, Burpee Gardening, and Arbico Organics).
Tarnished Plant Bugs & Stink Bugs: Tarnished plant bugs (Lygus lineolaris) and stink bugs (Acrosternum species and Euschistus species) will both feed on the young fruit. As the bugs penetrate the fruit with their needle-like mouthparts, they inject saliva that kills the plant cells around the puncture. They then suck the juices from the fruit. As the fruit continues to grow, depressed areas appear around the feeding sites. Homeowners use sprays of cyhalothrin (gamma or lambda) or zeta cypermethrin for controlling these pests. Keeping early-blooming weeds cut in the area where the apple trees are growing reduces the number of plant bugs.
Plum Curculio: The plum curculio (Conotrachelus nenuphar) is a native weevil that may attack apple fruit. The adult weevils spend the winter in protected areas near the apple trees. They return to the trees in the spring after three or four days when the temperature is above 70 °F. After petal fall, the female weevil will make a crescent-shaped cut through the fruit skin and insert an egg under the flap. Usually, the larva is killed by the rapidly growing fruit. The scar will show up at harvest. Infested fruit will become misshapen and often will drop to the ground. Removal of wild plum in the area and practicing sanitation around the apple trees will reduce the problem. Pick up prematurely fallen fruit and dispose of them. Insecticide sprays that are applied immediately after bloom may reduce plum curculio damage. Sprays with cyhalothrin (lambda or gamma) or zeta cypermethrin are used to manage plum curculios. Do not apply carbaryl spray to apple trees within 30 days after bloom. Fruit tree combination sprays with carbaryl can be used if more than 30 days after bloom.
Pests Attacking the Branches, Trunk & Roots
San Jose Scale: One of the most important pests of the branches is the San Jose scale (Quadraspidiotus perniciosus). The adult scale insect is about 0.1 inch in diameter. It has a grey cover that hides the insects. Scale insects have thread-like mouthparts that are inserted into the bark, and they feed on the sap. There are four generations a year in South Carolina.
A single female scale can produce about 400 young over a six-week period. The young are called crawlers and move to a new area. They then settle down, insert their mouthparts, begin to feed, and secrete the covering over their body. When populations are high, the crawlers may settle on the fruit, and their feeding produces red measles-like spots on the ripe fruit.
Heavy scale infestations can kill individual branches. The best control for scale insects is a thorough spray application of 2% horticultural oil on the trunk and limbs in the late winter or early spring. This should be applied before the leaf buds begin to open. During the growing season, either insecticide sprays, such as cyhalothrin (lambda or gamma) or zeta cypermethrin, or 1% horticultural oil sprays will kill the crawlers. Insecticide sprays will not kill the scales once the cover is secreted.
Aphids: Usually, aphids are considered a pest of the leaves. However, the woolly apple aphid (Eriosoma lanigerum) feeds on the bark of small twigs, around pruning cuts, and on the roots of apple trees. The feeding causes the tree to form knobby galls, which can occur on the twigs and roots. Heavy damage can reduce the vigor of the tree. Woolly aphids are covered with a mass of long wax filaments, which gives them their common name.
The above-ground aphids can be controlled with insecticide sprays (such as malathion or a fruit tree spray containing malathion) or horticultural oil sprays. These should be applied whenever colonies of the aphids are present. Root feeding colonies cannot be controlled.
Borers: Apple trees that are under stress from being recently planted, drought, or by other causes may be attacked by the flatheaded appletree borer (Chrysobothris femorata). This borer is found primarily on young trees. The adult beetles are about ½-inch long, somewhat flattened, and vary from dark metallic brown to a dull gray. The larvae are legless, yellow to yellowish-white, and have a broad, flattened area immediately behind the head. Mature larvae are 1½-inches long.
The larvae damage the trees by boring in the trunk and main branches. Initial attacks are usually on the sunny side of the tree. The galleries will be filled with sawdust-like frass or excrement. Infested trees will often have cracks in the bark that ooze sap. Eventually, the galleries can girdle the tree and cause the death of the tree.
Adult beetles are present from late spring to November. There is one generation a year. Vigorous trees will often produce enough sap to drown the larvae in the galleries. The best control measure is to keep the trees healthy and vigorous. Water trees weekly during periods of heat and drought.
Occasionally, apple trees will go into a slow decline. Close examination of the roots will show the damage from Prionus root borers (Prionus species). These borers may attack weak trees, and they may also attack young trees that are planted in an area that was recently cleared of hardwood trees. The larvae of this borer can survive for several years feeding on dead roots. Since the life cycle of this pest is at least five years, the larvae grow to a very large size. Mature larvae may be as large as a man’s finger. There is no control for this pest.
Though products are available at gardening stores for homeowners, many gardeners are not inclined to use pesticide applications for home fruit production. Instead, hobbyist gardeners may use bags to protect the fruit from pests and diseases. Clemson University has tested and is promoting the use of specialty bags that, if used properly, allow for the production of high-quality fruit with very little pesticide input. These fruit bags are recommended for use in a four-step fashion: (i) properly take care of your trees to minimize tree stress; (ii) protect the fruit from pests and insects between bloom and the day of bagging; (iii) enclose ½- to ¾-inch, green fruit (typically 3 weeks after bloom) with a specialty bag; and (iv) remove the bags approximately 3 weeks prior to harvest to allow the fruits to color properly For purchase information and use instructions please see: Clemson Fruit Bags or google this page using the keywords “Clemson Fruit Bags”.
Table 1. Insecticides for Use in Home Orchards to Control Apple & Crabapple Pests.
|Insecticide Active Ingredients||Examples of Brands & Products|
|Bt (Bacillus thuringiensis)||Bonide Thuricide Bt Concentrate
Monterey Bt Concentrate
Garden Safe Bt Worm & Caterpillar Killer Concentrate
|Spinosad||Southern Ag Conserve Naturalyte Insect Control Conc.
Bonide Colorado Potato Beetle Beater Concentrate
Bonide Captain Jack’s Deadbug Brew Concentrate
Ferti-lome Borer, Bagworm & Leafminer Spray Conc.
Monterey Garden Insect Spray Concentrate
Natural Guard Spinosad Bagworm, Tent Caterpillar &
Chewing Insect Control Concentrate
|Horticultural Oil||Ferti-lome Horticultural Oil Spray Concentrate
Bonide All Seasons Horticultural Spray Oil Concentrate
Monterey Horticultural Oil Concentrate
Summit Year Round Horticultural Oil Concentrate
|Malathion||Southern Ag Malathion 50% EC (Conc.)
Bonide Malathion Insect Control Concentrate
|Cypermethrin, Zeta||Gordon’s Bug-No-More Lawn & Garden Insect Control Conc.
GardenTech Sevin Insect Killer Concentrate
|Cyhalothrin, Gamma||Spectracide Triazicide for Lawns & Landscapes Concentrate|
|Cyhalothrin, Lambda||Bonide Fruit Tree & Plant Guard Concentrate (also
contains Boscalid & Pyraclostrobin – both fungicides)
|Carbaryl, Malathion, & Captan (fungicide)||Bonide Complete Fruit Tree Spray (Conc.)
Tiger Brand Fruit Tree Spray (Conc.)